The present invention relates to exhaust gas recirculation systems in an internal combustion engine, and, more particularly, to a bypass system for an induction venturi assembly in such exhaust gas recirculation systems.
An exhaust gas recirculation (EGR) system is used for controlling the generation of undesirable pollutant gases and particulate matter in the operation of internal combustion engines. Such systems have proven particularly useful in internal combustion engines used in motor vehicles such as passenger cars, light duty trucks, and other on-road motor equipment. EGR systems primarily recirculate the exhaust gas by-products into the intake air supply of the internal combustion engine. The exhaust gas which is reintroduced to the engine cylinder reduces the concentration of oxygen therein, which in turn lowers the maximum combustion temperature within the cylinder, and slows the chemical reaction of the combustion process, decreasing the formation of nitrous oxides (NOx). Furthermore, the exhaust gases typically contain unburned hydrocarbons, which are burned upon reintroduction into the engine cylinder, further reducing the emission of exhaust gas by-products that otherwise would be emitted as undesirable pollutants from the internal combustion engine.
When utilizing EGR in a turbocharged diesel engine, the exhaust gas to be recirculated is preferably removed upstream of the exhaust gas driven turbine associated with the turbocharger. In many EGR applications, the exhaust gas is diverted directly from the exhaust manifold. Likewise, the recirculated exhaust gas is preferably reintroduced to the intake air stream downstream of the compressor and air-to-air aftercooler (ATAAC). Reintroducing the exhaust gas downstream of the compressor and ATAAC is preferred due to reliability and maintainability concerns that arise if the exhaust gas passes through the compressor and/or ATAAC. An example of such an EGR system is disclosed in U.S. Pat. No. 5,802,846 (Bailey), which is assigned to the assignee of the present invention.
With conventional EGR systems as described above, the charged and cooled combustion air transported from the ATAAC is at a relatively high pressure, as a result of the charging from the turbocharger. Since, typically, the exhaust gas is inducted into the combustion air flow downstream of the ATAAC, conventional EGR systems are configured to allow the lower pressure exhaust gas to mix with the higher pressure combustion air before the combined flow is introduced in to the intake manifold. Such EGR systems may include a venturi assembly, which induces the flow of exhaust gas into the flow of combustion air passing therethrough. An efficient venturi assembly is designed to xe2x80x9cpumpxe2x80x9d exhaust gas from a lower pressure exhaust manifold to a higher pressure intake manifold. However, because varying EGR rates are required throughout the engine speed and load range, a variable orifice venturi assembly may be preferred. Such a variable orifice venturi assembly is physically difficult and complex to design and manufacture. Accordingly, venturi systems including a fixed orifice venturi assembly and a combustion air bypass circuit are favored. The bypass circuit consists of piping and a butterfly valve in a combustion air flow path. The butterfly valve is controllably actuated using an electronic controller which senses various parameters associated with operation of the engine. A bypass circuit can prevent excessive pressure losses in the combustion air circuit, which otherwise might occur during periods of high combustion air flow rates, such as at high engine speeds.
With a venturi assembly as described above, the maximum flow velocity and minimum pressure of the combustion air flowing through the venturi assembly occurs within the venturi throat disposed upstream from the expansion section. The butterfly valve is used to control the flow of combustion air to the venturi throat, which in turn affects the flow velocity and vacuum pressure created therein. By varying the vacuum pressure, the amount of exhaust gas induced into the venturi throat of the venturi assembly can be varied. However, the butterfly valve and electronic controller therefor can add complexity to the EGR system, increasing the chance for system failure and increasing the expense associated with repair.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the invention, an internal combustion engine comprises a combustion air supply, an exhaust manifold and an intake manifold. A venturi assembly includes an outlet connected and in communication with the intake manifold, a combustion air inlet connected and in communication with the combustion air supply, and an exhaust gas inlet connected and in communication with the exhaust manifold. A bypass fluid line is connected and in communication with the combustion air supply, and connected and in communication with the intake manifold, bypassing the venturi assembly. A bypass valve, controls flow through the bypass fluid line, the bypass valve being responsive to pressure differential on opposite sides of the venturi assembly.
In another aspect of the present invention, a venturi bypass system for recirculating exhaust gas in an internal combustion engine, comprises a venturi assembly having an outlet, a combustion air inlet and an exhaust gas inlet; a bypass line conducting combustion air around the venturi assembly; and a bypass valve positioned in the bypass line to open and close the bypass line in response to pressure drop across the venturi assembly.
In still another aspect of the present invention, a method of recirculating exhaust gas in an internal combustion engine, comprises providing an exhaust gas recirculation system including a venturi assembly having a combustion air inlet, an exhaust gas inlet and an outlet; transporting combustion air to the combustion air inlet; transporting exhaust gas to the exhaust gas inlet; and selectively controlling flow through the bypass line in response to pressure drop across the venturi assembly, thereby controlling the pressure drop across the venturi assembly.